Measuring the strain of equipment and infrastructure directly and continuously for a long time has been a long-standing issue. Strain gauges developed in the 1930s are still the main means for industrial use because of their ease of use, but because of their durability, system size, and power consumption, they are difficult to incorporate into equipment and infrastructure.
To solve the above problems, the winners have developed a semiconductor strain sensor that integrates a measurement bridge, amplifier, A / D converter, compensation circuit, temperature sensor, etc. into a 2.5 mm square CMOS semiconductor. The main performance is 1με distortion resolution and 3mW power consumption. These are performances that can solve the above problems, but actual use required modularization, advanced technology, componentization, and development of peripheral technologies for various applications. The winners were able to solve these problems and go to market under the name “STREAL” about 10 years after the principle was developed. Currently, applications are being studied in various fields such as infrastructure, processing machinery, and transportation equipment.
The strain measurement system was integrated on a 2.5 mm square chip ( Fig. 1). The characteristics of high-density semiconductors change when they are strained, but the problem was solved by various correction circuits and the layout of bridge circuits. Although the piezoresistive element that forms the bridge circuit has a large temperature dependency, a thermometer element was placed nearby to realize an automatic temperature correction function.
Fig.1 Iintegration image and IC chip appearance
To easily use this sensor, it was necessary to have a module that could accurately transmit the strain to the IC chip and easily handle it. Figure 2 shows the appearance of the module, and Table 1 shows the main specifications. This is a structure in which an IC chip is bonded to a 12mmL x 5mmW thin metal sheet and output via FPC. It can output both analog output and digital. The built-in temperature sensor can also be output and can be used as a simple thermometer. Depending on the arrangement of IC chips on a thin metal plate, a tensile and compression strain measurement module and a shear strain measurement module can be created separately.
Fig.2 Module appearance
Tabl1 Specifications (SRMS300NB0001)
Figure 3 shows how to use the module. Basically, a thin metal plate is bonded to the measured object using an adhesive. It is difficult to select a high-strength, long-life adhesive. Therefore, the winners are building a database of adhesives suitable for their application.
Fig.3 How to use the module
(4) Future plans
We are developing various components #1 that combine a unique flexure element and STREAL, and next-generation IC #2 with improved resolution to 0.1με.
The “STREAL”, which has unprecedented characteristics, has enabled advanced control, state monitoring and failure sign monitoring for industrial equipment and infrastructure. It is expected to breakthrough performance and safety improvements, optimize maintenance costs, and build a safe and secure society.
*1：Nikkan Kogyo Shimbun (‘19．11．15) Torque sensor with 0.5%crosstalk
*2：Nikkan Kogyo Shimbun (‘19．12．4) 0.1μεresolution strain sensor
*1 Fellow, Glosel Co., Ltd., System Solution Div.（Chiyoda-ku, Tokyo）
*2 Hitachi, Ltd., IT Platform Products Management Div. (Totsuka-ku, Yokohama)
*3 Fellow，Hitachi, Ltd., Research & Development Group(Kokubunji, Tokyo)
*4 Hitachi Automotive Systems, Ltd., (Hitachinaka, Ibaraki)
*5 Mmber, Hitachi, Ltd., Research & Development Group (Hitachi, Ibaraki)